Cyclohexylbenzyl compounds such as cyclohexylbenzene are useful intermediates in the production of a variety of other commercially valuable intermediates and precursors, such as biphenyl compounds (which, themselves, are useful intermediates in production of polyesters, plasticizers, and other polymer compositions, among other things) and phenol and/or cyclohexanone (which itself is a useful intermediate in, e.g., caprolactam for nylon production).
One of the most convenient means to produce cyclohexylbenzyls such as cyclohexylbenzene is hydroalkylation of co-fed benzene and hydrogen using a hydroalkylation catalyst, such as described in U.S. Pat. No. 6,037,513. Substituted cyclohexylbenzyl compounds, such as alkyl-substituted cyclohexylbenzyl compounds, may be formed by utilizing toluene, xylene, or another alkylbenzene in place of benzene in the hydroalkylation process.
Unfortunately, hydroalkylation offers little in the way of control of alkylation position. For instance, in the hydroalkylation of toluene to obtain methylcylohexyltoluene (MCHT), the reaction product will contain alkyl substitutions on both the cyclohexyl and the phenyl rings of the compound. While a hydroalkylation feed comprising both toluene and benzene could result in some cyclohexylbenzyl species having a methyl substitution on only one of the two rings, control as to which of the two rings have that substitution is still difficult, and furthermore, the reaction products would contain significant amounts of unsubstituted cyclohexylbenzene and the di-substituted MCHT species.
Furthermore, even among the MCHT species, it is difficult to control the positions of the alkyl substitutions on each ring. For instance, MCHT can be dehydrogenated to provide dimethylbiphenyl (DMBP). DMBP can readily be converted to an ester plasticizer by a process comprising oxidation of the DMBP to produce the corresponding mono- or dicarboxylic acid followed by esterification with a long chain alcohol. However, for certain uses, only particular positional isomers of DMBP are useful. For instance, 2,X′ DMBP (where X′ is 2′, 3′, or 4′) isomers are not preferred in a final product since, for example, diphenate esters having substitution on the 2-carbons tend to be too volatile for use as plasticizers. Even using a selective molecular sieve catalyst for the hydroalkylation step, the process tends to yield a mixture of all six DMBP positional isomers (2,2′, 2,3′, 2,4′, 3,3′, 3,4′, and 4,4′ DMBP), including up to about 20% by weight or more of the undesired 2,X′ DMBP isomers, which cannot easily be separated from unreacted MCHT by distillation due to an overlap in their vapor-liquid equilibrium properties.
There is therefore a need for a means of producing selectively alkylated cyclohexylbenzyl and biphenyl compounds, offering some control over the position(s) of alkyl substitutions in such compounds.
Additional references of interest may include U.S. Pat. No. 6,730,625; U.S. Patent Publication nos. 2014/0275605, 2014/0275606, 2014/0275607, 2014/0275609, 2014/0323782; and WIPO Publication No. WO 2010138248 A2. Further references include Bandyopadhyay et al., “Transalkylation of Cumene with Toluene over Zeolite-Beta,” Applied Catalysis A: General, 135 (1996) 249; Bandyopadhyay et al., “Transalkylation Reaction—An Alternative Route to Produce Industrially Important Intermediates Such as Cymene,” Catalysis Today, 44 (1998) 245; Mavrodinova et al., “Transalkylation of toluene with cumene over zeolites Y dealuminated in solid-state, Part I: Effect of the alteration of Broensted acidity,” Applied Catalysis A: General, 248 (2003) 181; Mavrodinova et al., Applied Catalysis A: General, 248 (2003) 197; Borodina et al., Petroleum Chemistry, 49 (2009) 66; and Lu et al., “Selective Hydrogenation of Single Benzene Ring in Biphenyl Catalyzed by Skeletal Ni,” ChemCatChem, 1:3 (2009) 369.